Gear wheels are a commonly known machine member and are of many different forms. Typically, they incorporate a rim of teeth, which are intended to cooperate either with corresponding teeth on adjacent gear wheels or with teeth on a toothed driving belt or the like. In the latter case these teeth are rule-shaped and have an axial extension allowing them to cooperate with transverse teeth on the driving belt.
Gear wheels are commonly made from cast iron or steel. The requirements on the design and machining of the teeth are always rigid. In the latter case, as mentioned above, when the teeth are rule-shaped, it is necessary that they are precision machined by milling or the like. Thus gear wheels are given an accurate shape, thereby cooperating in a satisfactory manner with the transverse teeth of the driving belt.
For gear wheels which cooperate with driving belts, it is often desirable that the gear wheel rim be provided with a flange on one or both side to ensure that the driving belt does not disengage from the gear wheel. Since the teeth require machining in a milling operation it is difficult or even impossible to provide the gear rim with the flange prior to the milling operation. In such cases use is therefore made of separate flanges, which after precision machining are fitted in grooves on the side of the gear rim. Gear produced in this manner and from the above-mentioned materials are heavy and expensive to produce.
It has long been a goal to be able to mold gear wheels directly without subsequent machining and from a low weight material. Different types of plastic material have been considered in the past, but the plastic material has the property that its coefficient of thermal expansion is much greater than that of steel and cast iron, whereby unacceptable dimensional changes will arise in connection with temperature changes, as other parts in the vicinity of the plastic material usually consist of steel or cast iron.